High pressure metamorphism in the Scourian of NW Scotland: Evidence from garnet granulites |
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| Authors: | David Savage Jane D Sills |
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| Institution: | (1) Environmental Protection Unit, Institute of Geological Sciences, Harwell Laboratory, Building 151, OX11 ORA Oxfordshire, England;(2) Department of Geology, University of Leicester, LE1 7RH Leicester, England |
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| Abstract: | Ultramafic and mafic granulites from Archaean gneisses in N.W. Scotland (the Scourian) show evidence of two periods of granulite facies mineral growth. The first produced a high pressure clinopyroxene +garnet±plagioclase assemblage at an estimatedP-T of 12–15 kb and 1,000° C. Uplift of the complex caused partial breakdown of the garnet by reaction with clinopyroxene to produce orthopyroxene +plagioclase ±spinel±amphibole symplectites, at an estimatedP-T of 10–14 kb and 800°–900° C. Garnet stability is shown to depend on both whole-rock Fe/Mg ratios and onP-T conditions. The pressures imply crustal thicknesses in the Archaean of least 35–45 km. |
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